Habitat analysis of bood grass (Isahcne miliacea roth ex roemet schult) under major wet land rice agro ecological units of Kerala

Blood grass (Isahcne miliacea Roth ex Roemet Schult) belongs to the family Poaceae is most dominant perennial weed species in the rice under cultivated and fallow situations. Habitat analysis of a weed species shows the interrelationship between the growth characters and adaptive mechanism that enable weeds to survive the changes in environment. Blood grass is one of the most dominant weed species in the wet land rice fields of Kerala with a relative density as high as 65 per cent during both first and second crop seasons as well as under both cultivated and fallow situations. Water and soil samples were collected and analyzed and correlated with dry weight of blood grass collected from the same spots to assess the habitat affinity of the weed. The sites selected from four major wet land rice agro ecological units of Kerala. Blood grass co- existed with rice crop, rice fallows, field bunds and irrigation channels but the growth was poor under deep flooded field conditions. The infested sites in general were acidic wherein the pH between from 4.2 to 5.9. Dry weight of blood grass had significant positive correlation with soil organic carbon in all agro ecological units. The dry weight of blood grass samples collected from the agro - ecological units varied between 90.8 g m^-2to 659.3 g m^-2. The available nitrogen, available phosphorus, available potassium in water recorded significant positive correlation while water level recorded significant negative correlation with the weed biomass production. The negative correlation with EC indicated that the blood grass growth was poor in saline soils.